1. Field of the Invention
This invention pertains to sharpening equipment, and more particularly to apparatus that sharpens a wide variety of cutting blades.
2. Description of the Prior Art
Rotary power mowers of various types are well known and are in widespread use. They vary greatly in size, complexity, and operating characteristics. However, all rotary power mowers utilize the common component of a rotary cutting blade. The blades are relatively long, narrow, and thin. A cutting edge is sharpened into each end of the blade. As the blade rotates under power from the mowing machine, the cutting edges shear vegetation.
The cutting edges of some rotary blades lie along substantially straight lines for their full lengths. A typical example of such a blade is shown at reference numeral 3 in FIGS. 1-3. The blade 3 has a longitudinal centerline 4 and a flat bottom surface 6, and opposed ends 34. There are a pair of cutting edges 8 at the ends 34, both of which lie along straight lines 10 that are substantially parallel to the longitudinal centerline 4. The cutting edges 8 and the straight lines 10 coincide. The blade further has back edges 2 opposite the cutting edges 8, and a top surface 80 opposite the bottom surface
Each cutting edge 8 is defined by the junction of the blade bottom surface 6 and a cutting surface 12. The cutting surfaces 12 intersect the top surface 80. The bottom surface 6 and cutting surface 12 subtend a cutting angle L. Each cutting edge 8 intersects an end 34 of the blade 3 at a tip 38. The tips 38 are especially important, because they are the portions of the blade that first come into contact with the vegetation being cut by the blade. There are an infinite number of imaginary lines 14 along the blade bottom surface 6 between each cutting edge 8 and the corresponding back edge 2. Flat blades such as the blade 3 are used to shear vegetation and expel it tangentially away from a mowing machine.
Other cutting blades have cutting edges that are not straight but instead lie along curved lines. The curved cutting edges are particularly useful for mulching the vegetation in addition to shearing it and expelling it. FIGS. 4-7 show a typical mulching blade 16 having five sections: a relatively long center section 26, a pair of angled sections 28 that slope downwardly and away from the ends of the center section 28, and a pair of end sections 30 on the ends of the angled sections 28. The end sections 30 lie in a plane that is substantially parallel to the plane of the center section 26. The center section has a bottom surface 22, the angled sections have respective bottom surfaces 48, and the end sections 30 have respective bottom surfaces 49. The center section has a top surface 84, the angled sections have respective top surfaces 86, and the end sections have respective top surfaces 88. The mulching blade defines a longitudinal centerline 92.
The mulching blade 16 further has curved cutting edges 18. Each cutting edge 18 lies along a respective curved line 20. The cutting edges 18 and lines 20 are generally parallel to the centerline 92 and are defined by the junctions of the bottom surfaces 22, 48, 49 of the blade sections with associated cutting surfaces 24. The cutting surface 24 intersects the top surfaces 84, 86, and 88. The cutting edges 18 also intersect the ends 40 of the mulching blade at tips 42. There are an infinite number of imaginary lines 32 on the mulching blade bottom surfaces between the cutting edges 18 and the back edges 90 of the blade opposite the cutting edges.
A routine task associated with rotary power mowers is sharpening the blades. For that purpose, a variety of mechanized equipment has been developed. For example, a division of Wall Enterprises, Inc. of New Whiteland, Ind., markets rotary blade grinding machines. Magna-Matic Corporation of Waldo, Wis., is a manufacturer of blade grinding and balancing machines.
Prior blade sharpening machines have not been entirely satisfactory. For one reason, they generally have been limited to sharpening blades with straight cutting edges, i.e., flat blades such as blade 3 depicted in FIGS. 1-3. That is because the prior machines had flat work surfaces of substantial area and lying in a single plane. The blades were supported on the work surfaces and manually fed lengthwise, i.e., parallel to the longitudinal centerline 4 of the blade 3, while in contact with a grinding wheel. The flat area of the work surface was satisfactory for straight edge blades, because no angular movements of the blade in space relative to the grinding wheel were required to grind the cutting edge.
On the other hand, the flat area work surfaces of prior blade sharpeners presented considerable difficulty with mulching blades, such as mulching blade 16 of FIGS. 4-7. That was because the mulching blade curved edges 18 required that the blades be fed crosswise in addition to lengthwise in order to properly grind the curved cutting edges. Simultaneous crosswise and lengthwise feeding of the blades was difficult to do, especially at the transitions between the various sections, such as the transitions between the center section 22 and the angled sections 28, and the transitions between the angled sections and the end sections 30. The prior sharpeners used relatively wide grinding wheels, such as one inch, which exacerbated the problem. Moreover, with a flat work surface of substantial area, the curved cutting edges of the different sections contacted the grinding wheel at different angular locations on the grinding wheel periphery. As a result, the cutting angles of the cutting edges at the different blade sections varied considerably. A uniform cutting angle was possible only by carefully imparting angular motions to the blade while lengthwise and crosswise feeding it.
An associated problem with the large flat work surface of a prior machine was that the work surface was cut out to make room for the grinding wheel. The work surface was therefore rather limber and prone to vibrate and create excessive noise during operation. A related problem with the cutout in the work surface was that the blade cutting edge was not supported directly in line with the transverse plane of the grinding wheel. It was very difficult to properly grind the tips of a blade using such a machine, because the cutting force of the grinding wheel required the operator to provide a resisting force. Even if the operator did not yield to the cutting force, the blade itself could bend because it was only cantilever supported by the work surface. Since the tips of the cutting edges are the most important part of the blade, any error in grinding the tips was quickly reflected in substandard mowing machine performance.
U.S. Pat. No. 5,329,731 shows an attachment for a grinding machine that facilitates sharpening mulching blades. The attachment has two flat work surfaces, each of substantial area, along which a blade is fed. However, the flat large area work surfaces limit the attachment""s usefulness when sharpening mulching blades having certain contours. In fact, some style mulching blades can not be sharpened at all when using the attachment of the U.S. Pat. No. 5,329,731. For some other mulching blades, even using the attachment of the U.S. Pat. No. 5,329,731 produces varying cutting angles on the blade cutting edges along different sections of the blade.
Yet another deficiency of prior sharpening machines concerns the grinding wheels and their mountings. In prior machines, the grinding wheels were mounted directly to the armature shafts of electric motors. Accordingly, the grinding speed was limited to the motor speed. However, many grinding wheels are capable of cutting at higher speeds than conventional motor speeds. Hence, the full cutting capabilities of the grinding wheels were not used. A related problem concerns the composition of the grinding wheels used with prior blade sharpeners. To compensate for the lower production obtained by, slower than usable grinding wheel speeds, prior sharpeners used harder than necessary grinding wheels. Such grinding wheels tended to burn rather than cut the metal from the blades. Further, the excessively hard grinding wheels easily loaded up with steel particles from the blades. Consequently, the grinding wheels had to be dressed periodically, which resulted in unproductive time.
Perhaps the biggest problem with prior blade grinding machinery was the lack of ability to grind blades of any length and configuration. For example, the grinding machine shown in U.S. Pat. No. 5,329,731 has upstanding posts that restrict lengthwise and even crosswise feeding of a blade past the grinding wheel. Consequently, the sizesand types of blades sharpenable on that machine are limited.
Thus, a need exists for improvements in blade grinding machines.
In accordance with the present invention, a blade sharpener is provided that is capable of properly and efficiently grinding both curved and straight edge blades without restriction. This is accomplished by apparatus that includes a work surface that supports a blade only along a single straight line that lies in the transverse plane of a grinding wheel and that is perpendicular to the blade cutting edge.
According to one aspect of the invention, the support line is a longitudinal line along a cylindrical surface on the top of a pedestal. The pedestal is mounted to a base that defines a base plane. The pedestal defines a pedestal plane that is perpendicular to the base plane and that passes through the support line. The pedestal plane is coplanar with the grinding wheel transverse plane.
A pivot plate is connected to the base for pivoting about a first axis. An electric motor and the grinding wheel are secured to the pivot plate. The grinding wheel axis of rotation is perpendicular to the support line and parallel to the base plane. The grinding wheel is relatively narrow, and it is driven by the motor. An adjustment mechanism pivots the pivot plate to adjust the position of the grinding wheel relative to the work surface, but the support line remains in the transverse plane of the grinding wheel for all positions of the pivot plate.
To use the blade sharpener, the pivot plate is adjusted to bring the grinding wheel periphery close to the work surface. A blade to be sharpened is oriented such that its longitudinal centerline is generally horizontal and perpendicular to the work surface and parallel to the grinding wheel axis of rotation. The blade cutting edge is also perpendicular to the work surface. The bottom surface at the end of the blade is placed on the work surface. The blade is fed crosswise, i.e., in a direction perpendicular to its longitudinal centerline and perpendicular to the grinding wheel axis of rotation, into contact with the grinding wheel periphery such that the cutting edge at the blade tip is sharpened. The support by the work surface directly under or very close to the cutting edge at the blade tip minimizes any problems associated with sharpening the tip. The blade is then fed lengthwise, i.e., parallel to its longitudinal centerline and perpendicular to the grinding wheel axis of rotation, along the work surface past the grinding wheel periphery, all the while being supported only by the single support line of the work surface. When an angled section of the blade, and the corresponding curve in the cutting edge, reaches the work surface, the single support line enables the blade to rise and fall relative to the grinding wheel while keeping the blade cutting edge always in contact with the grinding wheel and always supported directly in line with the grinding wheel. In that manner, blades of a wide variety of contours and cutting edges can be efficiently sharpened.
Further in accordance with the present invention, blades having cutting edges of unlimited length are sharpenable. The blade sharpener has no posts or other members that restrict the length of the blade cutting edge. Similarly, there is no crosswise restriction in the access of the blade to the grinding wheel.
It is a further feature of the invention that it takes full advantage of modern grinding wheel technology. As one example, the production rates available from high grinding wheel speeds now available are utilized by means of an updrive between the motor and the grinding wheel. Consequently, rather than being limited to the speed of the motor, the grinding wheel is rotated approximately 20 percent faster than in prior blade sharpening machines. At the same time, the grinding wheel has a hardness only slightly greater than that of steel blades. The combination of the relatively soft grinding wheel and higher grinding wheel speed results in rapid and clean cutting of the blade during the sharpening process. The tendency of burning metal, rather than cutting it, from the blade that results from using the prior hard grinding wheels at slower speeds, is eliminated. In addition to having higher production, the blade sharpener of the invention eliminates the need for a grinding wheel dresser.
According to another aspect of the invention, a flat work surface of substantial area is interchangeable with the single support line work surface. For that purpose, a mobile work table has a top plate from which depend a pair of parallel lugs. The lugs are spaced apart a distance slightly greater than the width of the pedestal that includes the single line work surface. A clamp is joined to the lugs. By placing the mobile work table over the pedestal and actuating the clamp, the large area flat work surface is retained on the blade sharpener The mobile work table finds use when sharpening flat workpieces such as straight rotary mower blades.
The method and apparatus of the invention, using a work support surface consisting of a single line, thus sharpens mulching blades in an efficient manner. The single support line enables blades of practically any size and contour to be sharpened, even though the cutting edges of the blade are perpendicular to the support line.
Other advantages, benefits, and features of the present invention will become apparent to those skilled in the art upon reading the detailed description of the invention.